1. Field of the Invention
The present invention relates to a heat-sensitive transfer image-receiving sheet and more particularly to a heat-sensitive transfer image-receiving sheet having a high sensitivity and little image defects. The invention also relates to a coating composition for producing a heat-sensitive transfer image-receiving sheet.
2. Description of the Related Art
Various heat-sensitive transfer recording methods have been heretofore known. In particular, a dye dispersion transfer recording method has been noted as a process capable of preparing a color hard copy having the closest image quality to silver salt photograph (see “Joho Kiroku (haado kopi) to sono zairyouno shintenkai (New Development of Data Recording (hard copy) and Its Materials)”, Toray Research Center, 1993, pp. 241-285, and “Purinta Zairyou no Kaihatsu (Development of Printer Materials)”, CMC, 1995, page 180). Further, this dye dispersion transfer recording method is advantageous in that it can be operated in a dry process as compared with silver salt photography and allows direct visualization from digital data that facilitates reproduction.
In the dye dispersion transfer recording method, a heat-sensitive transfer sheet containing a dye (hereinafter referred to as “ink sheet”) and a heat-sensitive transfer image-receiving sheet (hereinafter referred to as “image-receiving sheet”) are laminated on each other. Subsequently, the ink sheet is heated by a thermal head which is controlled in heat generation by an electric signal so that the dye in the ink sheet is transferred to the image-receiving sheet to make recording of image data. Cyan, magenta and yellow colors are then recorded imposed on each other to make transfer recording of a color image having a continuous color density change.
As the support for the image-receiving sheet to be used in this process there may be used ordinary paper that allows production of image-receiving sheet at a reduced cost. In order to compensate the cushioning properties of the support, the image-receiving sheet comprising such paper as a support normally comprises a layer having high cushioning properties such as foaming layer made of resin and foaming agent provided interposed between the support and the receiving layer to provide the image-receiving sheet with cushioning properties and enhance the adhesion between the image-receiving sheet and the ink sheet. However, since the related art image-receiving sheet has heretofore been produced from an organic solvent-based resin coating solution, the coating solution fills the foam and void in the foaming layer, making it impossible to obtain desired cushioning properties. Thus, problems occurred that white marks or density unevenness occur during image formation or the heat insulating properties of the foaming layer are deteriorated to cause calorie required for dye transfer to be diffused toward the back surface of the image-receptive sheet, resulting in the drop of sensitivity during printing.
On the other hand, the employment of a method involving the spreading of a water-dispersible emulsion on the support allows delicate roughness developed by foaming layer in the receiving layer to reflect directly on the surface shape of the receiving layer. For example, JP-A-2-265789 and JP-A-2005-62829 disclose a receiving layer formed by a water-dispersible emulsion. This receiving layer imposes little burden on the global environment. Further, the material required therefor is relatively inexpensive. However, these inventions are disadvantageous in that the use of such a water-dispersible emulsion causes the deterioration of sharpness.